In order to realize a coaxial transmission with a fixed transmission ratio, especially a transmission with a relatively large single stage transmission ratio, it is generally known to design an epicyclic gearing transmitting units with a fixed transmission ratio. In an ordinary epicyclic gearing mechanism, the design is limited by the conditions of transmission ratio, conditions of concentricity, conditions of assembling, conditions of adjacency, and the efficiency of the transmission.
In order to overcome the disadvantages of ordinary epicyclic gearing, epicyclic gearing of cycloid needle type have been proposed; but this requires special output mechanism, high precision work and is inconvenient in maintenance and repairing work. Moreover, the bearing of the epicyclic gear is under high stress and because of the limitation in design structure, larger bearings can not be used. In FIGS. 10 and 11 of U.S. Pat. No. 3,468,175, a transmission unit with a relatively large single stage transmission ratio and without the usual epicyclic gearing mechanism is disclosed. Thus the possibility to solve the above problems is offered. But in the structure of such patent there still exist, among others, the following problems: low transmission efficiency; heat is easily produced in the cam and the rolling member in meshing contact with the cam; and, in the meshing contact of the rolling member and the internal gear race, early wear of the guide groove, the roller member and the internal gear race produces additional heat during meshing. The main causes of those problems are (a) the linear speed of the meshing contact of the high speed cam and of the rolling member on the transmitting race is too high, (b) the rolling member and the guide groove i the radial direction of the transmitting race are in direct contact; when the rolling member is in radial motion at remote center position, there is some displacement of the contact position of the rolling member and the guide groove and displacement of the meshing position of the rolling member and the internal gear race. If the relative motion between the rolling member and the guide groove is pure rolling then the rolling member should have rotation in clockwise direction. If the relative motion between the rolling member and the internal gear race is pure rolling, then the rolling member should have in rotation the counterclockwise direction. However, the same rolling member cannot have clockwise and counterclockwise rotation simultaneously. Thus, this rolling member can be neither normal rolling nor normal sliding.